Collection of gas-borne dust particles by means of an aspirated sampling nozzle

The efficiency of collection of gas-borne particles by an aspirated sampling nozzle is investigated theoretically and experimentally. The efficiency is shown theoretically to depend on (a) the ratio of the velocity of aspiration into the sampling nozzle to the velocity of the undisturbed gas stream, and (b) the ratio of a length representing the distance of disturbance upstream of the nozzle to the range of a particle. The range is defined as the distance a particle would travel, before coming to rest, if projected into still gas with a velocity equal to that of the gas stream. In the range of conditions investigated experimentally, which included nozzles of 0.65 to 1.90cm diameter aspirating from turbulent gas streams, it is found that the length representing the upstream disturbance is a function of the diameter of the nozzle.